1. Field of the Invention
The present invention relates to a liquid crystal display device for projecting an image on a screen using a light valve element such as a liquid crystal panel module, and more particularly to a cooling technique for the liquid crystal panel module, a polarizing plate (a plate with a polarizing film), etc.
2. Description of the Prior Art
In a liquid crystal display device, room air outside the device is used for its internal cooling.
In the case of a conventional cooling method of directly blowing air to a liquid crystal panel module, dust floating in the air, cigarette smoke, and the like are stuck to a surface of the liquid crystal panel module when operated for a long stretch of time. The dust and the like sticking to the liquid crystal panel module may interrupt a pixel thereof because the size of the pixel is small (e.g. 10 to 30 μm square). If an image is projected in this state, the dust will be transcribed in the image as a shadow, as it is.
In other words, a projection lens is in focus on the liquid crystal panel module portion and accordingly, not only the image displayed on this liquid crystal panel module but also the dust or the like sticking in the vicinity thereof become the shadow in the projected image. Although the size and the location (the distance from the focal plane) of the dust actually affecting vary according to the F value of the projection lens, it is necessary to prevent the dust from sticking to the vicinities of the liquid crystal panel module, at any rate.
Further, the size of the liquid crystal panel module has been increasingly reduced for cost saving, and now, a liquid crystal panel module of 0.5 inch size comes into use, so that the heating density in the liquid crystal panel module becomes high.
Furthermore, in order to enlarge the area of the projected screen and to improve luminance thereof, the intensity of incident light on the liquid crystal panel module tends to be increased more and more, resulting in a rise in heating value. Accordingly, a raise in temperature of the liquid crystal panel module and of a polarizing film (plate) arranged in front and back of the liquid crystal panel module falls to be a problem, so that it is required to improve the cooling capacity of the liquid crystal panel module portion.
To meet this requirement, in JP-A-2002-357803 and JP-A-2002-296565 for instance, a cooling medium such as water is sealed or circulated in a light transmitting area of the liquid crystal panel module and the polarizing plate to improve the cooling capacity. However, in the case of this cooling method, since the light is transmitted through the cooling medium such as water, a distribution is generated in the refraction index due to density variation or flow velocity distribution caused by temperature distribution of the cooling medium, to cause a problem that the image is fluctuated, or distorted.
Further, in JP-A-2000-206507, heat radiation is improved by making the substrate material of the polarizing plate of sapphire having high thermal conductivity, so as to address the high-luminance liquid crystal display device. However, since this is a method of directly blowing air on the liquid crystal panel module and the polarizing plate to cool those, there has been a problem that the dust and the cigarette smoke contained in the cooling air stick to the surfaces of the liquid crystal panel module and the polarizing plate to deteriorate the image quality.